Mid-measure parameter changes

The group attributes can optionally be preceded by mid-measure
parameter changes.
This is not used very often, but the most common
use is to change the
clef
in the middle of a measure. There are only a few
other parameters that can be changed inside a measure:
alignrests,defoct
and
release.
The change is enclosed in double angle brackets.
After the opening angle bracket is the
context
to which the changes applies (score, staff, or voice),
followed by one or more parameter changes.

1: c; e; <<score clef=bass>> 2g;
bar

If there is more than one parameter listed, they are separated by semicolons.

<< staff clef = tenor ; defoct = 4 >>

If you wish to change parameters in more than one context, multiple
angle-bracketed items can be given:

If you specify "staff" or "voice" context, the specific staff(s) or voice(s)
to which the changes apply is based on which staff(s) or voice(s)
are being described on the input line. So in the example above,
the clef is changed to alto on staffs 2 and 3, and the defoct is
changed to 3 for voice 2 on both of those staffs. The release change
applies to the entire score.